Cigarette Smoking, Alcohol Consumption, and the Risk of Thyroid Cancer in Japan: The Japan Public Health Center-Based Prospective Study.

[BACKGROUND] Although cigarette smoking and alcohol consumption are established causes of cancer, most cohort studies and meta-analyses have reported inverse associations with thyroid cancer risk. However, epidemiologic evidence for this possibility is limited in Asia, where thyroid cancer histologic type differs from the West. In this study, we examined the association between cigarette smoking or alcohol consumption and the risk of thyroid cancer in Japanese.

[METHODS] We analyzed data of 101,849 Japanese included in the Japan Public Health Center-Based Prospective Study. Cigarette smoking and alcohol consumption were assessed at baseline using a self-administered questionnaire. Cox proportional hazards regression models were used to estimate the HRs and 95% confidence intervals (CI).

[RESULTS] During a mean 18.7 years of follow-up, we identified 232 incident cases of thyroid cancer. The multivariable-adjusted HRs (95% CIs) for current cigarette smoking with ≥20 pack-years compared with never-smoking were 0.65 (0.39-1.06) and 0.45 (0.23-0.88), respectively, combined for both sexes. After detailed adjustment for cigarette smoking, compared with no current alcohol consumption, HRs (95% CIs) were 0.90 (0.61-1.33) for any current consumption and 0.81 (0.33-1.97) for ≥300 g ethanol/week consumption combined for both sexes.

[CONCLUSIONS] We observed an inverse association between cigarette smoking and thyroid cancer in Japan. Although an inverse association between alcohol consumption and thyroid cancer is suggested, the CI was wide and included 1.

[IMPACT] Cigarette smoking was shown to be potentially inversely associated with thyroid cancer in Japanese, providing insights into risk factors in Asians. Further studies with larger sample sizes are needed to verify these findings.